The present invention relates to power and signal buses for electrical networks, and in particular to multi-layer cable systems providing combined power and signal connections to a network of electrical and electronic components.
The interconnection of multiple electrical or electronic components in a network requires a consideration of the requirements of the various components of the network and the environment in which the network will be installed. In the simplest such systems, only a conductor carrying power to each device is required. The device is “on” when power is distributed along the conductor, and is “off” when power is no longer maintained. No separate control signal lines are thus required. Multiple components may be maintained on a power network of this type by connecting components in series, in parallel, or in various combinations of serial/parallel networks as desired in order to meet operational requirements of the system.
The problems of interconnecting components becomes more complex when control signals must be directed to the various components separate from the distribution of power. The simplest control signal solution for this type of network, which also requires the greatest quantity of wiring, is to maintain a separate control line or lines to each of the components in the system. In order to reduce the quantity of wiring, many networks use a single control line that has a connection to each component in the network. If this arrangement is to be employed, however, some means of component addressing must be employed so that each element of the network can determine to which control signals it must respond. The most complex systems may require multiple control signal communications buses in addition to a power distribution system, even where an addressing scheme is employed. These types of systems will require considerable quantities of wiring in order to form all of the necessary connections even though addressing is employed to reduce the number of necessary control lines. Large quantities of wiring increases the cost of the network, not only due to the cost of the wiring itself but since the complex wiring increases the time involved in installing and maintaining such a system.
The simplification of power and signal interconnections on a network of components becomes even more important when the network is installed in an environment where available space and system weight is tightly limited. Examples of such a space include the cabin sections of aircraft and watercraft. The particular difficulty faced by the inventor hereof was the interconnection of a complex, multi-module light emitting diode (LED) lighting system in such an environment. Each lighting module of the LED system is connected to multiple control networks and to a power system. Using a standard wiring scheme would result in large bundles of wiring in order to implement such a network, rendering installation and maintenance difficult and time-consuming.
Flexible microstrip and stripline electrical connecting cables are known in the art. Generally speaking, a “microstrip” may be described as a flat strip of conducting material applied onto a dielectric, such as on a printed circuit board, or a flat strip of conducting material flanked by only one ground plane. A “stripline” may be defined as a flat strip of conducting material encased in a dielectric, or otherwise surrounded on both its upper and lower surfaces by a dielectric material or ground planes. These terms are sometimes used interchangeably, and the terms “stripline” and “microstrip” as used herein should each be understood to encompass both types of devices. While this technology is most often applied directly onto (or into) multi-layer printed circuit boards, it has also been applied in transmission lines located off of circuit boards as well. One commonplace application of this technology is in the area of high-frequency antennas or communications networks, particularly microwave systems. Microstrip and stripline connectors are popular in these applications because they reduce radiation leakage as would be experienced in co-axial or other types of connecting lines.
The general construction of a flexible stripline conductor involves multiple layers of conducting elements and dielectric elements. For example, U.S. Pat. No. 5,631,446 to Quan teaches a radio frequency (RF) flexible printed wiring board transmission line for connection strip transmission line microwave assemblies. The flexible transmission line includes a thin flexible dielectric ribbon sandwiched between a ground plane conductor on one side and a microstrip conductor on the other side. Flat cables having a greater number of conducting and insulating layers are also known; examples include the flat cable taught by U.S. Pat. No. 5,373,109 to Argyrakis et al.
The prior art also teaches means of connecting the various conductive layers of a flat cable to other cables or the components of a network. It is often desirable in certain applications for multiple connections to be made on a single side of such a flat conductor. This may be implemented by the use of “vias” formed through some of the flat cable's layering. In essence, a via is simply a hole through some of the cable's outer layers that allows access to a conducting layer within the cable. For example, Quan '446 teaches that vias formed in the transmission line at its ends allow connection of the ground and conductor strips from the same side of the flat transmission line. U.S. Pat. No. 6,020,559 to Maeda teaches a flat flexible cable with electrically insulating films on either side of the flat conductors, with a plurality of access openings through the films to the conductors. Alternative arrangements to the via approach for interconnections are also employed in prior art devices. U.S. Pat. No. 6,055,722 to Tighe et al. teaches a stair-step type arrangement of layers in a stripline flexible cable, with the individual ends forming the stair step arrangement available for separate connection to a printed circuit board.
The prior art flat transmission lines as herein described, while offering some advantages over traditional round cable in certain applications, are not optimized for use in applications where a combination of power and ground signals are required through a single, flexible flat cable. In particular, the interconnect mechanisms for flat cable taught in the prior art would not allow for a modular network, where individual components on the network could be easily connected and disconnected to a single flat cable providing both power and signal inputs. In addition, the interconnect mechanisms taught in prior art flat cables do not maximize the conductor area available to power and system ground conductors. Limitations on the conductor area for the power and ground conductors means that the overall width of the flexible cable must be increased in order to accommodate a given current level. In such a case, the flexible cable may by necessity become wider than the network components themselves, which increases the space required for installation of the components. The present invention overcomes these disadvantages and limitations of the prior art as explained below.